Method of making rubber articles by deposition



Patented Oct. 27, I931 PARKE n. WATKINS, or mom-n, AND ALBERT w. HOLMIBERG, or soon: omennnw JERSEY, AssIGNoRsTo NATIONAL INDIA'RUIBBER COMPANY, or BRISTOL, anomama e Sulphonated vegetable oil 35 UNITED, STATES PATEN'POFFICEA ISLA ND, A CORPORATION 01 RHODE ISLAND METHOD OF ,MA KING RUBBER ,ARTICLES BY. DEPOSITION no Drawing.

This invention relates to an improved method for forming an articleof rubber composition by depositing rubber "composition from an aqueous dispersion upon a form of the required shape. I

It is an object of this inventionto provide a method of forming articles of rubber composition, whicharticles have localized thickened portions, by depositing the rubber, from an aqueous dispersion of the same.

the preferred embodiment of the invention,,a form in the shape of the article, for instance, an overshoe, and made of. filtering or porousmaterial, for examplefunglazeol porcelain or earthenware, is immersed in an aqueous dispersion 'of' rubber and allowed to remain in contact therewith for a suflicient interval of time, to permit of the deposit of alayer of rubber composition of the thickness desired- In one example of the invention, rubber latex, the natural Water emulsion of .rubber obtained fromthe rubber trees,of a

concentration of about 35% solid constituents by weight, is combined with various types of mineralfillers, softeners, vulcanizing ingredients, stabilizing agents, etc. A specific compound employing a semi-cured .latex,

which may be used in carrying out the invention is as follows:

Rubber as semicured latex contain- Z i n c (ilm'ethylamine dithiocarbat 5 part by weight 5 .parts by Weight Kaolin 35 parts by weight Asbestine 15 parts by weight Glue '1 part by weight .1 part by weight parts by weight .8 cos. per

100 ccs. of 1 c0mp0und- Ammonium thiocyanate Water;

Sodium polysulphide ,2 In this composition, the kaolin and asbestine act as filling agents, the glue acts a's a stabilizer for'the dispersion, thesodium polysulphide functions as a thickener, and the ammonium thiocyanateaids in accomplishii g the thickening. The carbon black serves as a coloring agent, While the zinc oxide, aids in effecting vulcanization. Itwill be understood that other stabilizing, thickefiin gfiroloring. and vulcanizillg ingredients Application filed April 4, 1927. Serial N0. 180,933.

adapted for use in constructing a rubber shoe. v v t v In the operation'of' coatingthe form for a rubber shoe with rubber dispersion, the

porous form is immersed in the composition above described, whereupon Water-is with j drawn from the dispersion adjacent the form through the pores of the latter efl'ecting a segregation or collection of thickened disper- S1011 adhering to the form. The Withdrawal of water takes place toward the interior of the form while the latter is immersed and upon withdrawal thereof from the dispersion, elimination of Water from-the adherent mass takes place not only toward theinterior but also byexterior evaporation. The form is-Withdrawn from the dispersion after the desired thickness of deposit has been obtained and can be dried at room tempera-' ture, whereupon a smooth coating of the deposited rubber composition of uniform thickness is left thereon free from runs and other imperfections.

Localized thickened portions can now be builtupon the coating. This is accomplished by dipping a desired portion of the coated form, for instance, the sole or if a bead is to be constructed, then the upper section of the coated form, into-the dispersion. Upon withdrawal from the dispersion, these portions of the form, are then immersed in a coagulatin bath which serves tocoagulate the rubber o the deposited dispersion. The coagulated rubber is then washed with water which is preferably kept nearly neutral by continual or complete replacement with fresh water. Preferably some ofthe coagulant is allowed to remain on the coagulated material'to has-- ten the-coagulation of the nextlayer of rubi ber. The form is again dipped into the dispersion, then intofthe coagulant and then into the wash Water. This procedure of alternately dipping, coagulating and washing,

whereby a thickened deposit of rubber composition is rapidly assembled, is repeated until a localized deposit of the desired thickness is obtained. A suitable coagulant for use in the above described process is composed of equal parts glacial acetic acid and water, but other coagulants may be used such as aqueous formaldehyde or other acids or aldehydes. After the final coagulation, the coated form can be washed in an alkaline solution if an acid coagulant has been used to neutralize any remaining coagulant and is then dried, or alternatively, drying alone can be resorted to to remove the excess coagulant. As a variation in the process, coagulation can be effected by the use of vapors of acetic acid or of formaldehyde. This method is of advantage for the reason that possibility of the formation of runs is eliminated.

If a further coating of rubber composition is desired upon the entire article, the form with its built up layers of rubber composition can be again immersed in the dispersion of rubber, withdrawn and dried to provide a final coating of a thin film of composition. An advantage of the method is that the main body of the article having a smooth surface and free from runs can be rapidly built up of a uniform thickness or with slightly varying thickness in a single dipping operation by the filtration step, and the localized thick portions can then be conveniently formed by alternate dipping and coagulating.

The article thus formed is subjected to vulcanization and for the composition described, this can be effected at from 1 to 1 hours at 212 to 220 F. It will be understood that the time and temperature of vulcanization will vary with the particular composition used.

The form upon whlch the rubber article is built can be constructed of any porous material which is capable of absorbing Water by capillarity and which will permit of the removal of the built up article therefrom. Suitable forms are constructed of porous earthen ware", fibrous composition such as paper, textile: fabrics or felts, or they can be made of a composition containing porous or pore producing materials such as whiting, Tripoli flour, kieselguhr, clay, etc., bound together by a suitable binner such as hydrated paper pulp,'phenol aldehyde concentration product,

etc. The porous nature of various parts of the form can be varied so as tocause the deposit of a film of varying thickness.

The process is applicable to the manufacture of any article which is susceptible of being built up by deposition of rubber com.- position from an aqueous dispersion of the same.- finch articles may be rubber shoes,

1 gloves, footholds, etc. Some articles such as lmemens gloves are sub ected to use for which they must be resistant to high volta e electricity. Then again an article may e dryi constructed which must be primarily water resistant, or a combination of these qualities may be needed in the same article. In such a case it is contemplated to coagulate the original layer of rubber composition upon the porous form by the use of acetic acid, formic acid, formaldehyde, etc. If the deposited rubber composition is coagulated by immersing the same in liquid coagulant it is preferred to dry the outer surface thereof before coagulating. If coagulation is effected by vapors of coagulant the step of drying the surface of the deposit can be omitted. The deposit is subjected to the action of'the coagulant until the entire thickness thereof or as much as may be desired has been coagulated. Thebuilding up of a article by a combination of the steps of depositing by means of a porous form and by acid coagulation results in an article having an improved ber dispersion and with coagulant, and vu1-:

canizing.

2. 'The method of making articles of rubber com osition which comprises continuously building up a deposit of rubber composition of a porous form by maintaining the form in contact with a body of a ueous rubber dispersion and withdrawing t e dispersing agent through the form, building up additional deposits of rubber composition by alternately contacting localized portions of the deposit with a rubber dispersion and with coagulant, depositing an additional layer of rubber composition by contacting the previously formed'article with rubber dispersion, drying and vulcanizing.

3. The method oflmaking rubber articles which comprises building up the main body of the article by a continuous filtration deposit from an aqueous dispersion of rubber,

ized t 'cken portion on the main body by alternate deposit and coagulation. of the dispersion on such portion.

4. The method of making rubber articles .which comprises depositing a layer of rubber composition on a porous form by withdrawing the dispersing agent of an aqueous disperslon of rubber therethrough, drying the outer surface of the layer, partially at least coagulating the layer, building up local- 1e dispersthe de osit, and building up a localized thickened portions upon the'deposit by. alternate deposition of rubber com osition from an aqueous dispersion of rub rand coagulation therof, andvulcanizing.

Signed at New York, N. Y'., this th day of March, 1927.

PARKE H; WATKINS.

Signed at New York, N. Y;, this 30th day of March, 1927.

ALBERT W. HOLMBERG. 

